Blasting of rock bodies



Dec. 4, 1956 R. B. AlTGHISON El AL l/I BLASTING OF ROCK BODIES Filed June 15, 1954 RoBERT"f r c?u soN JOSEPH J. CALAMAN 9 a TT'ORNEY United States Patentl t BLASTING OF ROCK BODIES Robert B. Aitchison, New York, N. Y., and Joseph J. Calaman, Aurora, Minn., assignors to Union Carbide and Carbon Corporation, a corporation of New York Application June 15, 1954, Serial No. 436,763.

Claims. (Cl. 102-23) issue Patent No. 22,964, parallel to the vertical face of the rock body, charged with explosives, and simultaneously detonated by rows to break large quantities of ore fragments from the rock body. It has been found, however, that some rock bodies, such as taconite, are notorious for large quantities of big boulders lying at the surface of the formation or close thereto. The standard blasting practice, describedabove, has not satisfactorily broken these boulders or reduced their size. They have been lifted with the blast only to settle back again on the pile of ore after the blast. It has, therefore, been necessary to force these large masses from the area to the quarry floor and there reduce them by secondary reduction procedures, such as further blasting and the like. Such operations are very costly, potentially hazardous and inefl'icient.

It is, therefore, the prime object of the present invention to provide a method of blasting such diflicult rock bodies which will not require further secondary reduction of the fragments.

Other aims and objects will be apparent from the following description and appended claims.

In the drawing:

Fig. 1 is a plan view of a portion of a rock body, showing the arrangement of blasting holes employed in the practice of the method of the present invention;

Fig. 2 is a partial sectional view taken along the line 2--2 of Fig. 1;

Fig. 3 is a partial sectional view taken along the line 22 of Fig. l at a time shortly after the beginning of the primary blast; and

Fig. 4 is a partial sectional view, taken along the line 22 of Fig. 1, a short time after the beginning of the synchronized satellite blasts.

In accordance with the present invention, and referring to the drawing, at least one spaced row of primary blast holes 12 are first pierced vertically in the rock body 14 parallel to a face 16 along which rock material removal is desired. A plurality of relatively smaller diameter satellite blast holes 18 are pierced around each of the primary blast holes 12 to a depth relatively shallow compared to the depth of the primary blast hole but deep enough to insure fragmentation of the large surface masses of rock. Each of the primary and satellite blast holes are loaded with explosive charges 21 and 22, respectively, and then stemmed.

The positioning of the plurality of satellite blast holes 18 around each of the primary blast holes 12 is determined by the position of cracks 19 on the surface of rock body 14. As shown in Figs. 1 of the drawing, the satellite holes are so positioned around the associated primary hole to accomplish the maximum fragmentation of the surface boulders 20 formed by these surface cracks.

The sequence of detonating primary blast hole charges, or rows of such charges, may be varied in accordance with procedures well known to the art. The time delay between the detonation of a primary blast hole charge and its plurality of associated charges may vary up to about 50 milliseconds, best fragmentation results having been. encountered where the delay time was sufiicient to allow a substantial surface doming condition to develop after detonation of the primary change before the detonation of the plurality of associated satellite charges.

It has been found that when the satellite charges are simultaneously detonated at a short period of time, in the order of a few milliseconds, after the simultaneous detonation of a rowof the primary charges, the large masses of surface rock are reduced and the need for secondary reduction of these bodies is eliminated.

It is believed that this surface fragmentation, unattainable with prior art blasting methods, is accomplished by virtue of the fact that the primary blasts cause a doming of the surrounding surface of the body, such as. shown in Fig. 3 of the drawing, together with vertical cracking 24 of the body caused by the expansion resulting from the primary blast. Thereafter, at a time up to about 50 milliseconds after the primary blast, while the surface is still in the expanded (domed) condition, the satellite blasts are simultaneously detonated and produce the further cracking 26, shown in Fig. 4 of the drawing, which reduces the large surface masses of rock so troublesome to the prior art.

The method of the present invention has been employed in blasting large masses of taconite ore. Inone such operation, two parallel rows of seven 6 /2 inch diameter primary blast holes, each primary hole being about 40 feet in depth and surrounded by a plurality of 1.25 inch diameter satellite holes 4 to 5 feet in depth, were charged and detonated. The primary holes in each row were disposed with 19 feet between centers and the distance between the rows was also about 19 feet. The rows of primary charges were detonated at 16 millisecond intervals and plurality of satellite charges were detonated simultaneously about 3 milliseconds after its associated primary charge.

The primary and satellite blast holes may be pierced by any means known to the art, but it has been found that the thermal rock piercing method disclosed in U. S. Reissue Patent No. 22,964 to C. J. Burch provides a method for piercing highly suitable blast holes in heat spallable materials, such as taconite and the like, in a minimum of time and with greater overall efiiciency than mechanical drilling methods. In such thermal piercing method a blast hole is pierced in a rock body by directing an intensely hot, high velocity, oxy-fuel flame against the body to be pierced to spall off particles while concurrently introducing water into the flame zone where it flashes to steam and ejects the spalled particles from the hole as pierced. In this manner the rock piercing blowpipe is progressively introduced into the pierced hole until a blast hole of the desired depth is obtained.

What is claimed is:

1. In the art of blasting difiicult-to-fragment rock bodies, the process which comprises, providing at least one row of substantially vertical primary blast holes in said body, said rows being substantially parallel to a face of said body; providing a plurality of smaller diameter substantially vertical satellite blast holes positioned in proximity with and around each of said primary blast holes, said satelliteholeshaving a shallowdepthrelative to the depth of said primary blast holes; charging each of said primary and satellite blast holes with "an'explosive charge; successively detonat-ing, in the order of their distance from said face of said body, each rowof s aiclprimar'y explosive charges; and detonating each plurality of satellite charges up to about 50 milliseconds after, the detonation of the proximate primary charge but before the detonation of the next row of prirnary charges.

-2. A method of blasting difiicult tmfragment rock bodies having substantial surface cracking comprising, providing at least one row of substantially vertical primary blast holes in said body, said rows being substantiallyparallel to a face of said body; providing a plurality of smaller diameter substantially vertical satellite blast holes positioned in proximity with and around eachof said primary blast holes, saidsatellite holes havinga shallow depth relative to the depth of said primary holes; charging each of said primary and satellite blast holes .with an explosive charge; successively detonating, in the order of their distance from ,said face of said body each row ofsa id primary'explosive charges; andde'tonati ng-each plurality of satellite charges up tofabout 50 millis'econds after the detonation of the proximate primary charge but before the detonation of the next row of primarycharges.

3. A method of blasting difficult to-fragment rock bodies having substantial surface cracking comprising, providing at least one row of substantially vertical primary blast holes in said'body, said row being substantially parallel to a face of said body; providing a plurality of smaller diameter substantially vertical satellitlblashholes positioned in proximity with and around each of saidlprimary blast holes, said satellite holes having a shallow depth relative to the depth of said primary blast holes; charging each .of said primary and satellite blast holes with an explosive charge; successively detonating, in the order of their distance from said face of said body, each rowv of said primary explosive charges; and detonating each plurality of satellite charges at such time after; the detonation of said proximate primary charge that the surrounding portion'of said body is in the domed condition,

'but before the detonationof the next row ofprimary charges.

"at-A method of blasting difficult-to-fragment r0612 bodies having substantial silrface cracking to form surface boulders comprising, providing at least one row of substantially vertical primary blast holes in said body, said rows being substantially parallel to a face of said body; providing a pluralityof smaller diameter substantially vertical satellite blast holegpositioned :in proximity with and around each of said primary blast holes, said satelliteholeshaving a shallow depth relative to theldepth of said primary blast hole;-charging eachof-said ,prim ary and satellite blastholeswith an explosive charge; 'suc-, e yr e cnat p ,,inn hc de c ztl si idi tasce from said face of said body, each row of sai d primary explosive charges; and --det0nating each-plurality of satellite charges up to about milliseconds after the detonation of the proximate primary charge but before the detonat tion of the next row of primary charges. I

5; Atmethodofblasting a body .of taconite rock having substantial surface cracking comprising, providing at least one rowofsubstantiallyverticul primary blast-holes in said b ody, said rows being substantially parallel y-to a a o aid. o y; P id n a pl l ty of a d am.-

eter substantially verticalsatellite blast holes positioned inproximitywith and around each of said. primary bla t holes, said satellite holes having a shallow depth relative to the depthpfsaid primary blast holes;, char,g ing Q39)! of said primary and satellite blastholes with an explosive charge; successively detonating, in the order of theindis: tanc'e ,fromsaid faceof said body, each row of said pri? mary;e xpl osive charges; and detonating each,plurality ;of satellite. charges up to about 50 ,milliseconds after the detonation of the proximate primary charge but before thedetonation of the -next row of primary charges.

ReferencesCited in the file of'this patent Engineeringand Mining Journal, vol; 155, N051, pages 92:951- ;(;January 1954);1N0. 3, paget97, (March; 1954;), ,(Gopyin'rscientific Library.)

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